The present invention relates to gas compressor-expanders wherein power is generated or refrigeration is effected utilizing the compression and/or expansion of a gas as in Stirling engines or Stirling chillers, and more particularly to gas compressor/expanders having a seal device for preventing lubricating oil from ingressing into a working space wherein a gas is compressed or expanded.
The fields of cutting-edge technologies, such as biotechnology and electronic devices, in recent years involve a pressing need to develop techniques for preserving various samples of materials at cryogenic temperatures. Attention has been directed especially to gas compressor/expanders, such as Stirling chillers, as means for realizing cryogenic temperatures for wide use in coolers for infrared sensors or superconductive devices, biomedical freezers or chillers, etc.
Such compressor/expanders comprise a piston or displacer (hereinafter referred to collectively as the xe2x80x9cpistonxe2x80x9d) housed in a cylinder, connected to a piston rod and reciprocatingly movable within the cylinder for compressing and/or expanding a working gas, provided around the piston rod is a seal service for preventing lubricating oil in a mechanism chamber (crank chamber) from ingressing into a cylinder space at the rear of the piston.
FIG. 8 shows a gas compressor/expander having a conventional seal device and comprising a housing 112 formed with a crank chamber 111, a cylinder 101 attached to the housing 112 for compressing or expanding a gas, and a piston 102 housed in the cylinder 101 reciprocatingly movable and connected to a crank mechanism (not shown) within the crank chamber 111 by a piston rod 103, cross guide 104 and connecting rod 105. The piston rod 103 extends through a partition wall 99 separating a space 106 at the rear of the piston from the crank chamber 111 and is provided with a seal member 107 for preventing lubricating oil in the crank chamber 111 from ingressing into the rear space 106.
Used as the seal member 107 is a lip-type seal member having a U-shaped section and a higher sealing property against a flow from the crank chamber 111 to the rear space 106 than against the opposite flow. Unlike seal members having no directionality in sealing property, such as slipper seals having a resin ring on the slidable face, lip-type seal members have an excellent sealing property in one direction and are widely used in hydraulic mechanisms, etc.
However, unlike the hydraulic mechanism wherein one side of the seal member is always in contact with lubricating oil, the gas compressor/expander is not designed to positively supply lubricating oil from the crank chamber toward the seal member so as to prevent ingress of the lubricating oil into the working space to the greatest possible extent, presenting the problem that marked wear occurs on the seal member.
Although countermeasures are therefore taken as by applying grease or like lubricant on the contact face of the seal member in advance, the lubricant applied to the seal member is gradually removed by reciprocating strokes of the piston rod, so that the seal member still wears away markedly to entail the problem of shortening the life of the machine. Especially in the case where the seal member is directional in sealing property, the grease or like lubricant applied initially is scraped off toward the side of lower sealing property with the reciprocating movement of the piston rod to result in a noticeably impaired life.
On the other hand, JP-A No. 87854/1989 discloses a seal device, as shown in FIG. 9 herein, and comprising a seal member 107 provided, at one side thereof toward a piston 102, with an intermediate chamber 108, and a second seal member 109 opposite to the seal member 107 in the directionality of sealing property and positioned between the intermediate chamber 108 and the piston 102. With this seal device, the intermediate chamber 108 is maintained at an internal pressure equivalent to the lowest pressure of a space 106 at the rear of the piston, so that the internal pressure of a crank chamber 111 is always higher than that of the intermediate chamber 108, whereby the seal member 107 is tightly pressed into contact with the outer periphery of a piston rod 103 to exhibit a high sealing property.
We have found by experiments that seal members, such as lip-type seal members, having directionality in sealing property act to send gas toward the direction of lower sealing property. With the seal device of FIG. 9, accordingly, this action lowers the pressure of the internal chamber 108 further below the lowest pressure of the piston rear space 106. When the pressure difference between the crank chamber 111 and the intermediate chamber 108 increases considerably during a continuous operation, the seal member 107 is pressed against the outer periphery of the piston rod 103 with an excessive pressure due to the pressure difference to cause marked wear on the seal member 107. This results in the problem that lubricating oil ingresses into the intermediate chamber 108 from the crank chamber 111 and further into the rear space 106.
Further, if the pressure difference between the highest pressure of the piston rear space 106 and the pressure of the intermediate chamber 108 increases considerably with a continued operation, the pressure difference causes the working gas to gradually leak out of the rear space 106 onto the crank chamber 111 via the intermediate chamber 108, consequently entailing the problem of impairing the ability of the gas compressor/expander.
In view of the foregoing problems encountered with the gas compressor/expander including a seal member which has a higher sealing property against a flow from the mechanism chamber (crank chamber) toward the piston rear space than against a flow in the opposite direction, an object of the present invention is to give a longer life to the seal member by minimizing the wear on the seal member and to prevent impairment of the performance of the gas compressor/expander by minimizing the leakage of the working gas from the rear space into the mechanism chamber.
The present invention provides a gas compressor-expander which has a space in the rear of a piston within a cylinder for compressing or expanding a gas, and a mechanism chamber provided with a power transmission disposed therein, a partition wall being provided between the piston rear space and the mechanism chamber and having a rod slidably extending therethrough for interconnecting the piston and the power transmission and a seal device surrounding the rod, the seal device comprising:
a first seal member 93 having a higher sealing property against a flow from the mechanism chamber toward the piston rear space 21 than against a flow in the opposite direction for preventing lubricating oil in the mechanism chamber from ingressing into the piston rear space,
an intermediate chamber 91 provided in the vicinity of the first seal member 93 at one side thereof toward the piston rear space and forming around the rod 22 an annular space having a radial dimension larger than the thickness of a lubricating oil film formed on a surface of the rod,
a second seal member 95 disposed in the vicinity of the intermediate chamber 91 at one side thereof toward the piston rear space for preventing working gas in the piston rear space from ingressing into the intermediate chamber 91, and
a communication channel 96 for causing the intermediate chamber 91 and the mechanism chamber to communicate with each other.
In the gas compressor-expander of the present invention described, the intermediate chamber 91 and the mechanism chamber are held in communication with each other by the communication channel 96, whereby the intermediate chamber 91 is maintained at approximately the same pressure as the mechanism chamber. This eliminates the likelihood that the pressure difference between the intermediate chamber 91 and the mechanism chamber will become excessive, permitting sliding contact of the first seal member 93 with the outer periphery of the rod 22 under a suitable pressure. As a result, the first seal member 93 exhibits a satisfactory sealing effect to prevent the lubricating oil in the mechanism chamber from ingressing into the piston rear space 21 and to diminish the wear on the first seal member 93, consequently obviating leakage of the working gas from the rear space 21 into the mechanism chamber and preventing impairment of the capacity of the gas compressor-expander.
Incidentally, even if lubricating oil from the mechanism chamber is left unremoved by the first seal member 93 and forms an oil film around the rod 22, the oil film becomes discontinuous in the intermediate chamber 91. This obviates the likelihood of the lubricating oil ingressing into the piston rear space 21.
Filter means, when provided at an intermediate portion of the communication channel 96, precludes the lubricating oil, lubricating oil vapor, water vapor, etc. within the mechanism chamber from ingressing into the intermediate chamber 91 by way of the channel 96.
With the gas compressor-expander having the seal device of the invention described, wear on the seal member is minimized to give a prolonged life to the seal device, and the leakage of the working gas from the piston rear space into the mechanism chamber is minimized to prevent impairment of the ability of the compressor-expander.
Preferably, a lip-type seal member is used as the first seal member 93, whereby a high sealing effect is available against a flow from the mechanism chamber toward the piston rear space. The second seal member 95 can be a seal member having no directionality in sealing property, which diminishes an excessive pressure drop of the intermediate chamber 91 due to the gas sending action of the second seal member 95.
According to a specific embodiment, the communication channel 96 is provided at an intermediate portion thereof with opening-closing means, e.g., a pressure control valve 98, for permitting passage of the working gas upon the pressure difference between the intermediate chamber and the mechanism chamber exceeding a predetermined value.
According to the specific embodiment, the opening-closing means operates to maintain the pressure of the mechanism chamber at a level higher than that of the intermediate chamber by the predetermined value, consequently holding the first seal member 93 in intimate contact with the outer periphery of the rod 22 under a suitable pressure for the seal member to produce a satisfactory sealing effect.
The present invention provides another sealing device comprising:
a first seal member 901 having a higher sealing property against a flow from a mechanism chamber toward a space 21 in the rear of a piston than against a flow in the opposite direction for preventing lubricating oil in the mechanism chamber from ingressing into the piston rear space,
an intermediate chamber 902 provided in the vicinity of the first seal member 901 at one side thereof toward the mechanism chamber and forming an annular space around a rod,
a second seal member 905 provided in the vicinity of the intermediate chamber 902 at one side thereof toward the mechanism chamber and having a higher sealing property against the flow from the piston rear space toward the mechanism chamber than against the flow in the opposite direction, and
an oil reservoir 903 provided between the second seal member 905 and the intermediate chamber 902 and capable of holding the lubricating oil to be sent in from the mechanism chamber,
the distance from the oil reservoir 903 to the first seal member 901 being smaller than the stroke length of the rod 22.
With the gas compressor-expander having the seal device of the invention described, a specified amount of lubricating oil is collected in the oil reservoir 903 by the reciprocating movement of the rod 22, and the rod 22 reciprocatingly moves in the oil reservoir 903, whereby the lubricating oil is supplied to the sliding surfaces of the first seal member 901 and the rod 22. This minimizes wear on the first seal member 901, giving a prolonged life to the seal device.
Preferably, the oil reservoir 903 is held in communication with the mechanism chamber by an oil return channel 904, through which an excess of the lubricating oil sent into the reservoir 903 is returned to the mechanism chamber.
When the device described is used, the lubricating oil from the mechanism chamber will not be collected in the oil reservoir 903 in a quantity more than is necessary, with the result that an oil film of suitable thickness can be formed on the outer periphery of the rod.
Further preferably, a lip-type seal member is used as the first seal member 901 and/or the second seal member 905. The first seal member of the lip type produces a high sealing effect against the flow from the mechanism chamber toward the piston rear space. Further the lip-type seal serving as the second seal member affords a high sealing effect against the flow from the piston rear space toward the mechanism chamber.